This invention generally relates to optical sensors, and more specifically, to staring optical sensors.
A staring optical sensor is usually a two-dimensional focal plane mosaic of photodetectors, each of which generates an electric current representing the intensity of light incident on a given area of observation, referred to as a pixel and representing one unit of resolution. Typically, the area behind each photodetector is used for electronic circuitry to amplify and multiplex the detector signal.
In a high resolution staring optical sensor, the photodetectors are quite small and are located very close to each other, with no or only very little space between adjacent detectors. As a result, the distance between centers of adjacent detectors, referred to as the center-to-center spacing, is quite small. As the center-to-center spacing is reduced--either by using smaller detectors or by locating the detectors closer together--the space behind each detector for the required electronic circuitry functions is also reduced.
Increasing the spacing between detectors while keeping the size the individual detectors fixed, increases the available area or space for the required electronic circuitry, but also introduces undesirable gaps between detectors. With a sensor having such gaps, the image of a target of interest that falls within a gap between detectors would be invisible to the sensor until that image moved onto one of the detectors.
Various approaches are used to decrease the pixel size in an optical sensor while still providing adequate space behind each photodetector for the necessary electronic circuitry. For example, with one arrangement, the pixels in the sensor are divided into groups and one photodetector and an associated electrical circuitry are provided for each group of pixels. In the operation of the sensor, a mirror, referred to as a toggle mirror, is used to scan, or toggle, the pixels of each group, one pixel at a time, over the photodetector for that pixel group.
A toggle mirror, however, is relatively heavy and the operation of the mirror may consume a significant amount of power. Furthermore, some optical sensors include several focal planes, and when a toggle mirror is used to shift the image incident on the sensor, the toggle mirror causes the image to shift globally over all of the focal planes of the sensor. Under some circumstances, though, such sensors operate more effectively if the image is not toggled on some of the focal planes of the sensor, or if the image is toggled differently on different focal planes.